The present invention relates to the filling of syringes with a liquid such as a medicine or other injectable product, and more particularly to a system for automatically and simultaneously filling each of a plurality of syringes with a predetermined amount of the liquid.
In the past, the filling of syringes with liquid product has been done individually for each syringe, typically being carried out either totally manually or with the aid of a machine that required at least manual control. The most basic method for filling a syringe is to insert the end of a hollow needle attached to the syringe into a container of the liquid product. The plunger on the syringe is withdrawn until the barrel of the syringe is observed to be filled with the desired amount of product.
Variations of this method have involved the use of metering devices to control the amount of liquid drawn into the syringe. For example, U.S. Pat. Nos. 3,875,979 and 3,907,009 disclose metering devices that include adjustably positioned gauge plates that limit the distance that the plunger can be extracted from the barrel of the syringe. These devices merely provide assistance in regulating the amount of liquid that fills the syringe, and do not eliminate or reduce the need for manually effecting the filling process for each syringe.
More recently, the filling approach has involved the use of a pump to provide the liquid product under pressure to the syringe. By opening a valve connected between the pump and the syringe, the pressurized liquid is allowed to enter the syringe and push the plunger outwardly. When the proper amount of liquid is in the syringe, the valve is closed. Although this approach does not require the manual withdrawal of the plunger to fill the syringe, it still does not reduce the need for manual assistance. More specifically, the operator must remain present to monitor the filling and to close the valve at the appropriate time.
It will be appreciated that there are two significant limitations associated with each of the foregoing syringe-filling techniques. The first of these is the requirement for the continued presence of a human operator during the entirety of the time that each syringe is being filled to either effect or control the filling operation. Secondly, since the syringes are filled one at a time, there are practical limitations on the production rate, i.e. the number of syringes that can be filled in a unit time period. Typically, a skilled and experienced operator can only fill about a dozen syringes per minute using the foregoing techniques.
An automated device for filling syringes is disclosed in U.S. Pat. No. 3,935,883. In this device, the piston of a large-volume pumping syringe is connected to a reciprocal driving motor. The cylinder of the pumping syringe is connected to a bulk source container by one check valve and to the syringe to be filled by another check valve. In operation, the piston is withdrawn from the cylinder by the driving motor to draw liquid into the cylinder from the container. On the return stroke, the liquid is pumped out into the syringe. By adjusting the position of an eccentric member connected between the piston and the driving motor, the length of its stroke and hence the amount of fluid pumped during each stroke can be varied.
While the automation provided by this device is helpful in reducing the need for manual input during the entire filling operation, it does not overcome the second limitation discussed previously. That is, each syringe is still filled on an individual basis. Consequently, the practical limitation on the rate of filling continues to be a factor.